a. Field of the Invention
This invention relates to a novel cross-linked type of hydrophilic acrylic polymer. Such polymers are useful in physological applications and are particularly useful in manufacturing hydrophilic contact lenses.
B. History of the Prior Art
In the prior art, cross-linked hydrophilic acrylic polymers are known which were particularly suitable for applications wherein physiological contact with the body is desired. These prior art hydrophillic polymers however have several disadvantages. One disadvantage is that an initiator or catalyst, which is frequently a toxic compound, is required to initiate and control polymerization of the hydrophilic acrylic polymer. Purification of the polymer is then required to remove any remaining catalyst or initiator. In addition, prior art hydrophillic acrylic polymers are not sufficiently uniform to provide sufficiently predictable swelling and expansion when the polymer is exposed to an aqueous liquid.
While attempts were made in the prior art to form hydrophilic acrylic polymers suitable for physiological use without catalysts or initiators, such attempts were generally not satisfactory since they involved initiation with ultra-violet or gamma radiation which was not commercially practical. In addition, it was not recognized that a more uniform less toxic polymer structure would be obtained if catalysts and initiators were not used.